Various amplifiers and power supplies are implemented using Envelope Elimination and Restoration (EE&R) techniques. The Kahn amplifier represents one such implementation of the EE&R techniques. An exemplary EE&R system is shown in FIG. 1. As shown, the desired signal 100 is synthesized from a constant amplitude variable phase RF signal 102, and a baseband signal representing the envelope amplitude 104. Additionally, the baseband envelope is applied to the Vdd supply 106 of an RF amplifier 108. Generally, the Kahn amplifier operates in saturation, and the saturated power is varied by changing Vdd. There is also a class of amplifiers referred to as “Adaptive Bias” amplifiers. Like the EE&R systems, there are variable power supplies on one or more of the amplifier supply connections; unlike EE&R, an “Adaptive Bias” amplifier receives an RF signal with its envelope.
Typically, EE&R amplifiers use an expensive and complex switching variable power supply. The requisite variable supply must be efficient, and very fast. To be efficient, it needs to employ switching. Switching speed needs to be much higher than the baseband bandwidth, making it expensive. The switching spurs appear as out of band spurs in various EE&R systems. Also, the variable power supply needs to have rise/fall times and delays much faster than envelope transition times. These factors contribute to the overall expense and complexity of variable switching power supplies.
In the past, multiple power supplies have been proposed in lieu of the variable power supply used in EE&R systems, but in such embodiments discrete and abrupt switching occurs between supplies. These approaches can cause switching discontinuities and steps.
A need therefore exists for improved amplifier and power supply configurations that improve operating efficiencies while lowering fabrication costs and complexity.